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| Organic Semiconductor Conference 2005: summary of Day Two | |
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Technion University: Dr Nir Tessler Developing materials for LEDs Dr Tessler presented new large-band gap cross-linkable polymers for use as host materials in LEDs. Covion Green PPV has a PL efficiency of 70%. When dispersed into the novel polymer matrix and cross-linked (made insoluble), the efficiency remains high at 65%. The combined system is useful for processing since the emissive layer can be patterned by UV exposure through a mask and removal of the non-exposed area with a solvent wash. Dr Tessler is CTO of Peptronics Ltd, a start-up company developing electronic polymers based on peptide linkages. In biological systems, complex polymers are constructed from arbitrary sequences of amino acids. These amino acid building blocks contain a biologically active function and a peptide linkage, which allows them to be polymerised with other amino acids. If the biologically active component is replaced with an electrically active component (based on an aromatic system), electronic peptide polymers of arbitrary length and complexity may be built up by exploiting the peptide linkages. A sequence of polymers containing thiophene active units bound using peptide linkages were synthesised. The band gap and photoluminescence peak of the polymers scaled with chain length showing that conjugation was preserved through the peptide linkage - essential for electronic action. Different building blocks have different properties, for example electro-optic activity or film forming function. Since peptide polymers can be created out of arbitrary sequences, polymers with the required function can be built by selecting the appropriate building blocks. In the biological field, synthesis and selection of polymer sequences with useful characteristics is done automatically by machine. This is also applicable to electronic polymers based on peptide linkages where novel sequences can be automatically synthesised and tested for PL efficiency, for example. Other properties, such as the ability to form films, are more difficult to test automatically. Peptide polymers with PL efficiencies from 15-50% have been demonstrated but EL efficiencies are still below 1%. Plextronics: Dr Troy Hammond A versatile platform technology to improve performance in organic electronic devices Plextronics is a three year old start-up company with 22 staff based in Pittsburgh, Pennsylvania. It develops and manufactures (on kg scale) materials for use in the organic electronics field. Plextronics has been designing new hole-injection layers based on polythiophene. Hole-injection layers are necessary to planarize the ITO surface, to transport hole and to block electrons in LEDs. Commonly used HILs are acidic, soluble only in water and have issues with stability and reproducibility. Plextronics HILs are soluble in organic solvents and non-acidic. Solvent based systems are more compatible with the active layers used in LEDs and PV devices and the acidic nature of HILs has been linked to device degradation. The performance of an HIL system can be judged on parameters such as work function, resistivity, hole mobility and solvent compatibility. These features impact organic display performance and manufacturing. HIL conductivity is controlled through the choice of conducting polymer and dopant and the ratio and formulation of the system. Conductivities between 10-8 and 102S have been achieved. The Plextronics HIL reduces the surface roughness of ITO from 3-5nm rms to 1.4nm rms. The work function of the HIL can be controlled through component and formulation choice - formulation can change the work function by 0.5eV. The morphology of the HIL also has a strong bearing on device performance. NUKO70: Professor P. Kathirgamanathan Elamates: A turn-key solution to OLED manufacturers NUKO70 manufactures rare-earth chelate materials for use in small molecule OLEDs. The company markets fluorescent, phosphorescent and ion fluorescent materials for use as emitting layers. NUKO70 also produces hole injecting, hole transporting, hole blocking and electron transporting materials as well as non-toxic host materials. Blue, red and green emissive compounds are available. Elam9363 is a hole-injecting/buffer material with a superior lifetime to CuPc, a lower operating voltage than 2-TNATA and a lower evaporation temperature than CuPc. E246 is a high mobility electron transporting material. Devices using E246 show three times as long lifetime as those using Alq3 as well as a lower operating voltage. Using both E9363 and E246 together provides improvements in lifetime and operating voltage as compared to CuPc and Alq3. NUKO70's compounds are well protected by patents at the major offices. Sensient Imaging Technologies: Dr Olaf Gelsen Organic semiconductors - a materials platform for applications from OPC drums to solar cells Sensient is a material supplier for the Organic Semiconductor Industry. It provides a forming platform for wide range of technologies, and has experience in the development, manufacturing and supplying of OSC (organic semiconductor) materials for OLEDs and OPVs. Sensient also produces synthetic dyes that could be used in inkjet printing on paper, plastic or food. For the OPC market, Sensient produces high purity CGM (charge generating materials) and CTM (charge transporting materials). ST 10/10.x (TiOPc) and ST 16/1 (TPD) can be supplied in kg. These are also the materials that allowed a natural move to the OLED platform: ST 10/13 (CuPc) and ST 16/7 (α-NPB). Sensient established four development directions: Hi-TG HTMs (hole transporting materials), phosphorescent systems (emitters, matrix materials from evaporable to wet processable), electron transporters - hole blockers, and blue emitters. As an HTM the company used Li 228 (TG = 147°C), showing high efficiency OLEDs. Using the Sensient proprietary host F1015, the red phosphor SP445 gave higher efficiency for the same brightness when compared to SP445 in CBP. Olaf presented a phosphorescent blue device with excellent efficiencies and simple device structure. On its way to supplying materials for the OE (organic electronics), Sensient develops new technologies for conductors, dielectrics, semiconductors to be used in manufacturing passive and active components for organic ICs. The company has recently released a laser-convertible polymer. The printine compound (sulfur substituted polyacetylene) is an insulator (10-14S/cm), soluble in organic solvents and has good film forming properties. A 60 mW laser converts the insulator to a completely insoluble conductor (102 S/cm) with high stability against environmental stress. Aixtron: Bastian Marheineke OVPD - Paving the way to full colour OLED display mass production Aixtron offers large-scale deposition method of SM (small molecule) organic materials and high-resolution mask technologies for making OLEDs for backlight, full colour displays and lighting applications. The method benefits from an advanced deposition process control, high deposition rates and excellent accuracy, stability, and reproducibility. Conventional SM evaporation takes place from the bottom to top, that is the evaporated source is placed under the mask-aligned substrate. Pioneered by Stephen Forrest at Princeton University, the OVPD (organic vapour phase deposition) technique utilises nitrogen to transport the small molecules through showerheads placed on top of the mask-aligned substrate. The method offers a very elegant way for growing successive layers (multi-layer structure). At a given source temperature, the deposition rate can be controlled by changing the flow of the carrier gas. The CCS (close coupled showerhead) technology leads to a uniform flow with very low material waste. OVPD is a flexible process, using up to 12 evaporation sources, and offers fast and precise layer switching. A major advantage of the OVPD method comes from the precise control of the doping concentration that leads to optical confinement of charges (through graded doping) or work function engineering (through graded electrical doping). Varying the OVPD process parameters can also tune the morphology of the deposited films, and therefore the interfaces between layers. The Gen2 OVPD comes with in-situ mask alignment. The Precision Masking for Full Colour Displays, already qualified in LCD manufacturing, is integrated as a bottom module to the OVPD chamber. The mask comes in contact with the Motherglass, arrangement that shows no bowing or distortion, and needs 30s for the alignment procedure at 450µm away from the substrate. To prevent the heating of the mask (due to its proximity to the 300-350°C showerheads), the Motherglass is actively cooled by a Cooling Chuck controlled by an external chiller. Engaging the fluid dynamic modelling, Bastian showed results for the heat transfer and distribution, which confirmed flat temperature profiles enabling stable and reproducible process conditions. OTB Display: Dr Bas van Rens Progress in building the first in-line PLED manufacturing system Part of the OTB Group, OTB Display offers solutions for PM (passive matrix) and AM (active matrix) display backplanes using P-OLEDs (polymer LEDs) and SM-OLEDs (small molecule OLEDs). It provides complete solutions from product design to full-scale production. The strength at OTB is the in-line production machine, which will be completed within a very short time frame. The Philips PolyLED acquisition enables OTB to further strengthen its offering. With the ultimate goal of producing 32-inch in-line TVs, the company focuses on improving its front-end (PM and AM backplanes) and back-end (mono P-OLED to 19" - 32" full colour P-OLED and SM-OLED) technologies. OTB Display relies on its expertise in complete manufacturing and integrates as many processing steps as possible into one production line (in-line processing). The substrate treatment and the front-end printing are performed in a conventional way, but the next steps (cathode deposition and thin film encapsulation) are performed in the company's 'in-line PLED' facility. This has a LEGO-like construction simplicity and minimises the substrate handling, giving the same history for all products. Bas underlined the causes of possible failures during the printing process, like crooked or weak nozzles, and even missing nozzles. The ink formulation is extremely important for in-pixel layer formation, and Bas discussed a few ways to obtaining good filling of the whole pixel and constant layer thickness after drying. printed systems: Prof Arved Huebler Electronics produced by mass printing: state of the art and challenges printed systems manufactures mass printed electronics based entirely on polymer materials. The company was founded in 2003 as a spin-off from the Chemnitz University of Technology, Germany. It has eight employees and is financed by revenue. printed system uses offset printing to deposit conductive, semi-conductive and insulating materials to build electronic circuits. Conventional paper is used as the substrate, making the process compatible with standard four-colour printing. Transistors are made with PEDOT/PSS is as a conductive material for electrodes and interconnects, F8T2 as the semiconducting active layer and a custom insulator. Since all components are printed and based on plastics, manufacturing is extremely cheap and the final product is environmentally friendly and suitable for recycling. The transistors are stable in the long-term and meet functionality guarantees. Products based on this technology have been demonstrated, including a keypad suitable for games and toys and an electronic ID system suitable for intelligent playing cards or ticketing. The printed systems are cheap enough to be used in throwaway advertising. The electrodes that interface between the printed system and external electronics can also be printed, for example a simple USB port for connecting to a PC. The printed source-drain electrodes require good homogeneity and sharpness. This is particularly difficult to achieve when small channel lengths are desired for high frequency electronics. Channel lengths of 20 or 50µm yield electronics that runs a rate of only several Hz. printed systems are working with 25µm channels at present. A fully offset printed functioning ring-oscillator circuit has been demonstrated but yield is low at present. Inca Digital: Bill Baxter Experience with high precision X-Y inkjet systems Inca Digital produces inkjet printers for large substrates, which replace traditional screen-printing systems. The company has recently been acquired by Dainippon Screen and is now focusing on the deposition of organic electronic materials. Inkjet printing is gaining market share in the traditional printing market since it can produce arbitrary output without the need to make new screens or masks. The market is predicted to be worth €1.3bn in 2010. Inca's flat substrate printers have deposition accuracies of around 20µm. Mr Baxter presented a photograph of highly accurate columns of UV cured ink drops. These were deposited over 30 passes from an Inca printer with a print speed of 1.35 m/sec but show no drop misalignment and good uniformity. Inca flat substrate printers have throughput speeds of 120 m2/h. Single pass systems are being developed for roll-to-roll style processing, capable of printing 6000 m2/h for the printed corrugated board market. The needs of commercial printing and organic electronics material deposition are different. Organic materials use different solvents and require very high accuracy of drop placement and drop size. Conventional printing needs low cost systems, high print speeds and tolerance to negligent operation. However, the knowledge developed for conventional printing in terms of printers, deposition physics, automatic maintenance systems and high volume materials handling has applications in the organic electronics world. DuPont Teijin Films: Julie Friend The latest developments in polyester film for flexible electronics DuPont Teijin Films is a leading name in manufacturing flexible substrates for organic electronics industry. Apart from being commercially available, the flexible substrates need to have a low coefficient of thermal expansion and low shrinkage (at upper processing temperatures), moisture resistance, smooth and clean surfaces, and show resistance to solvents. DuPont believes in working closely with its customers and helping them to make the appropriate film choice for preferred manufacturing routes, knowing that films 'straight off shelf' may not have the required properties. The company produces two types of bi-axially oriented and semi-crystalline films: PET (Melinex Polyethylene Terephthalate) with a Tg of 78°C, and PEN (Teonex Polyethylene Naphthalate) with a higher Tg of 120°C. Most polymers will shrink or expand when heated above the glass transition temperature Tg. The heat-stabilised versions of the two films allow for higher processing temperatures of 150°C for PET and 180-220°C for PEN. This treatment greatly reduces the shrinkage levels, allowing materials to be utilised in application areas where stability and multiple registration steps are a key requirement. All polymer substrates pick up moisture to varying degrees. However, bi-axially oriented semi-crystalline films have better moisture resistance than amorphous films. Experimental studies on controlled moisture pick-up show a 33ppm dimensional change in a given direction per 100ppm moisture. The humidity pick-up is also thickness dependent, with thinner films picking up moisture faster. The smoothness of the substrate is extremely important, for example, to achieve integrity of barrier and ITO coatings. DuPont uses White Light Interferometry and Atomic Force Microscopy to analyse the planarity of the films, both techniques giving fully complementary outputs. Optically clear Melinex (with an incorporated filler) has a roughness of 2.48nm, where as the standard PET is 65nm. A significant roughness reduction is seen for Teonex as well. A planariser could bring the roughness down to 0.6nm for both Melinex and Teonex films. Cleanliness of the flexible surfaces is affected by air borne debris or scratches. DuPont is developing a family of planarising coatings that would give balanced properties (hardness, smoothness, flexibility) based on application. Vitex Systems: Dr Lorenza Moro Barix technology: Thin film encapsulation for flexible electronics Vitex develops technologies that protect organic devices from moisture and oxygen, and can be used in virtually any application involving OLEDs, OPVs and OTFTs. The company offers multi-layer barrier against water and oxygen, and multi-layer encapsulation that acts as an environmental barrier and could be manufactured by thin film deposition processes. Dr Moro described Vitex as the 'complete solution provider', offering Barix encapsulation (in future also for flexible plastic displays) and flexible glass substrates. Despite its apparent redundancy, the multi-layer barrier offers many advantages. It is a combination of organic/inorganic layers, with the organic part offering planar and smooth surfaces, and the inorganic part being the actual barrier to water and oxygen penetration. The sandwiched structure enables a long moisture and oxygen diffusion path. It is transparent and therefore suitable for top-emitter architectures and for displays. Being processed at low temperatures, it complies with the manufacturing requirements of organic materials. The average substrate temperature is far bellow 100°C, exceeding it only for a few seconds during curing. Using Ca coupons (for OLED), Dr Moro presented the impact of particles (extrinsic defects) on barrier. She traced defects created by particles incorporated in the encapsulation film, but they could be avoided by performing the encapsulation in-line with the OLED deposition. Vitex wants to improve the Barix multi-layer barrier process to allow mass manufacturing. They look at reducing the number of layers and sealing the edges. Dr Moro showed an OLED encapsulated with a reduced number of layers whose performance didn't degrade after 1000 hours of operation. Performing the edge seal in the encapsulation of PM Displays on glass, Dr Moro saw less than 10% pixel shrinkage and no increase in leakage current after 500 hours at 60C/90% RH. The company investigates the encapsulation of full colour PM and flexible AM displays. Issues like plasma damage or angular dependence need to be overcome when changing from monochrome to full colour displays. Lorenza showed a typical life time of 500 hours in 60C/90% RH for Barix coated devices (of full colour inkjet PLED display on glass). The light angular distribution of top emission devices depends on colour and thin film optical properties of the encapsulation. The optimized Barix coating offers no spectral shift for RGB pixels (no change in angular dependence of light output). Read the summary for Day One of OSC-05 Conference proceedings  You can purchase the full proceedings from OSC-05. The proceedings are provided on CD-ROM and consist of the slides (over 800) from all 23 presentations.
Format: CD-ROM, in PDF format with 20-user licence The proceedings cost £100.00 +VAT. 
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